Module 26
Malfunction Indicator Light (MIL) / Freeze Frame
Author: Grant Swaim
E-mail: sureseal@nr.infi.net
URL: www.tech2tech.net
Phone: (336) 632-9882
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Physical Address: 220-4 Swing Rd
Greensboro, NC 27409
Last Update: April 2000
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On Board Diagnostics—General Overview
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MIL / Freeze Frame
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Comprehensive Component Monitor
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Page 26-1
26 MIL / Freeze Frame
26.1 MIL General Information
The OBD-II system changed the way the MIL reports malfunctions. Prior to
OBD-II, the MIL would illuminate only when a malfunction was detected. It
would stay illuminated for the duration of the trip, but would reset on the next restart and not illuminate unless the malfunction reoccurred.
The MIL on an OBD-II equipped Honda works a lot differently. The MIL may
not come on with the first occurrence of a malfunction and may stay on even if
the fault is no longer present.
The MIL on OBD-II vehicles can only be used to notify the driver when a malfunction is occurring with a system that would effect the emissions of the car.
Other systems on the car that do not effect emissions cannot use the MIL to notify
the driver of problems, but must use a separate light. When a transmission DTC is
set it will illuminate a transmission MIL (usually the D4 light). If, however, the
transmission malfunction is one that could effect the emissions of the car the
OBD-II MIL is illuminated also.
26.1.1 MIL Illumination
Screen Capture 26-1
When the OBD-II system detects a malfunction, and
sets a hard fault code, the MIL is continuously illuminated for the remainder of the trip. When a pending DTC is set, the MIL will not be illuminated.
A new feature with the OBD-II system is a blinking
MIL. If a condition exists that could damage the
catalytic converter, the MIL will blink until the condition does not exist.
The MIL is commanded on or off by the ECM. You
can see the MIL command status by using an OBDII compliant scan tool. Screen Capture 26-1 shows a car whose MIL has been
commanded off. The MIL should initially illuminate for 2 seconds when a Honda
is first started to check the bulb. If the MIL is not illuminating for the bulb check,
check the ECM MIL command. If the command is for the MIL to be on but it is
not, the problem is external of the ECM. It is not all that uncommon to find a used
car that has had the light or wiring tampered with to keep the light
from illuminating.
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This manual printed 4/9/00 from the file pgmfiobd_002.
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26.1.2 Extinguishing the MIL
Prior to OBD-II the MIL would reset on each new trip and not illuminate unless
the malfunction still existed. The OBD-II MIL is extinguished only after a specific set of conditions have been met. There are two different set of conditions,
which are:
26.1.3 Misfire and Fuel System Malfunctions
For misfire or fuel system (LT FT) malfunctions, the MIL is extinguished if the
fault does not recur when monitored during three subsequent sequential drive cycles in which conditions are similar to those under which the malfunction was
first determined. The RPM must be within 375, the load conditions within 20%,
and the same warm-up status.
26.1.4 All Other Malfunctions
The MIL is extinguished after three subsequent sequential drive cycles during
which the monitoring system responsible for illuminating the MIL functions
without detecting the malfunction and if no other malfunction has been identified
that would independently illuminate the MIL.
26.2 Freeze Frame
26.2.1 Freeze Frame General Overview
A new feature with the OBD-II system is the ECM's ability to take a snapshot
(freeze frame) of certain engine parameters when a DTC is set. This feature is a
valuable diagnostic tool when working with intermittent problems. This information can be used by the tech to try and recreate the conditions that were present
when the original malfunction occurred. It is recommended that you try to operate
the vehicle within 10% of the recorded parameters to recreate a malfunction.
26.2.2 Freeze Frame Writing Strategy
OBD-II regulations only require that one freeze frame be used, however a manufacturer can make as many available as they want. Honda, like most manufactures, only captures one set of engine parameters. GM OBD-II systems capture as
many as seven freeze frames.
The freeze frame will take a snap shot when the first hard DTC (turns on the MIL)
is set. Subsequent DTCs will not have a freeze frame associated with them unless
they have a higher priority. If another DTC is set that has the same priority, the
freeze frame will not be overwritten. All DTCs have the same priority except for
any misfire or fuel system (LT FT) DTCs which are on the same priority level but
above all other DTCs
 All Rights Reserved 2000 Sure Seal Products Inc
This manual printed 4/9/00 from the file pgmfiobd_002.
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26.2.3 Freeze Frame Information
OBD-II regulations specify the parameters that are to be included in a freeze
frame (shown in table below). Each manufacturer can add more parameters, but
must include this base set of parameters. It is common to find more freeze frame
parameters available when using an OEM scan tool, Vs a generic OBD-II scan
tool. Screen Capture 26-2, was taken using a Mastertech in the generic OBD-II
mode.
OBD-II Requirements
Honda Freeze Frame
DTC That Was Stored.
Calculated Load Value
Engine RPM
Screen Capture 26-2
Fuel Trim Value
Fuel Pressure (if available),
Vehicle Speed
Engine Coolant Temperature,
Manifold Absolute Pressure
Fuel System Status
26.3 Service Issues
The new freeze frame feature can be a valuable diagnostic tool. To get the most
use from this information you need to understand a two simple principles.
26.4 Record the Freeze Frame Parameters!
For the freeze frame data to be of any use to you, you obviously need to know
what it is. You need to get in a habit of writing down the freeze frame data when
it is available. If you follow the old practice of clearing the DTCs from the ECM
and driving the car to see if the problem reoccurs, you will be erasing a lot of
valuable information. Always record the freeze frame information before you
clear the codes, even if you intend on resetting the codes and letting the customer
drive the car to see if it will set the same DTC. The malfunction may occur intermittently and the stored freeze frame information may have the only useful information you have on the problem!
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This manual printed 4/9/00 from the file pgmfiobd_002.
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Keeping track of freeze frame data on many different vehicles may get to be a
challenge. You can write the information down and file it in your customer's file,
or record it in the customer's computer records. A better way may be to store the
scan tool screen captures into a special database program for later retrieval.
There are several programs like this that are available, but my favorite is the AES
Wave program. The folks at AES can sell you a serial cable for virtually any scan
tool or digital storage oscilloscope (DSO). The cable is used to send the screen
capture into the AES Wave database program which can be installed on a desktop
or laptop computer. When you save a screen capture into the program you add all
the vehicle information for easy retrieval in the future. All the screen captures
used in these training modules are stored in the AES Wave program.
The nice thing about being able to save an unlimited amount of screen captures is
you can save any screen capture from any DSO or scan tool, not just use it to store
freeze frame information. Different DSOs and scan tools may take a different serial cable, but all the screen captures can be saved in the same AES Wave database program. You could even store digital photographs in it if you want ! Once
you master how to work with image files, you can then start attaching them to email and send the screen captures to anybody else in the world with e-mail.
26.5 Clearing Freeze Frame Data
The Honda OBD-II system will only write one freeze frame. As covered earlier
in this module, a freeze frame will be overwritten if a DTC with a higher priority
is set. The thing to remember here is the ECM cannot take another snapshot if the
freeze frame is holding data. After you record the freeze frame data, you need to
clear the DTC and its freeze frame. You can always remove power to the ECM to
reset these, but you will loose any adaptive learning the ECM may have in memory. It is best to clear the DTC and freeze frame with a scan tool. When you clear
the DTCs using an OBD-II compliant scan tool you will be clearing the DTCs,
clearing the freeze frame, and resetting the status of all "once-per-trip" monitors
to incomplete.
 All Rights Reserved 2000 Sure Seal Products Inc
This manual printed 4/9/00 from the file pgmfiobd_002.